1. Field of the Invention
The present invention relates to an oil seal which is a kind of a sealing apparatus, and a process for producing the same.
2. Description of the Conventional Art
As for a conventional process for reducing sliding resistance of a seal lip in an oil seal, (1) a process for reducing press force with respect to a shaft which is opposite in sliding, and (2) a process for reducing a friction coefficient of a lip slide part have been known.
However, as for the process (1), since a lip length is set to be short according to reduction of press tension force with respect to a shaft, a lip design to have following-up property to the shaft under high eccentricity in well balanced state is hard, and thus there is a problem that sliding resistance cannot be largely reduced. Further, as for the process (2), a process to coat various kinds of a film on a lip slide part has been considered. However, there is a problem that sliding resistance may increase in a quite early stage due to an initial abrasion of a coated film.
Further, as for a process to attach a fluororesin sheet to a lip slide part, there is a problem in durability of attachment between a lip base material rubber and the resin sheet so that sealing property may be damaged (refer to Japanese Utility Model Publication No. H6-16771 and Japanese Utility Model Publication No. H5-57523).
Further, as for a process to coat a lip slide part with polytetrafluoroethylene (PTFE), since PTFE is not chemically reacted on a rubber surface, binding property to a rubber is inferior, and thus durability cannot be obtained (refer to Japanese Utility Model Publication No. H6-35740 and Japanese Patent Application Laid Open No. H9-68011). In addition, surface hardness of a rubber may increase so as to increase surface roughness, and thus sealing property may be damaged (refer to Japanese Patent Application Laid Open No. H8-48800).
Further, an oil seal made by coating a resin layer, which is made by binding a dispersing element as a solid lubricating agent with a binding resin (a binder), on an air side slope in a lip slide part has been known. However, this conventional technique provides a structure in which a lip slide part contacts to a shaft by only a resin layer in order to reduce a friction coefficient. Thus, a contacting state of a lip slide part to a shaft is unstable, and thus there is a problem that a sealing property may decrease. Further, in this conventional technique, the binder is a polyimide resin or an epoxy resin. However, these resins are conventionally used for processing a fluororesin. Thus, when these resins are used on the surface of a seal lip made of a rubber like elastic material, a coating layer becomes to be hard, and thus there is a problem in durability (generation of breaking or peeling of the coating layer) at the time of sliding (refer to Japanese Patent Application Laid Open No. H7-217746).
In addition, although present inventors provide various kinds of a coating layer applied for a lip slide part, all of these coating layers are different from the content of the present invention (refer to Japanese Patent Application Laid Open No. S63-8428, Japanese Patent No. 3,316,993 and Japanese Patent Application Laid Open No. 2003-213122).